Apparatus for directing air flow and sound waves

ABSTRACT

An enclosure, in the form of a mold, attached to the hood or cowling of a vehicle engine, having an air inlet integral with the hood or cowling, combines with the hood to form passages for flow of combustion air to the engine as it passes through the mold. The mold provides cold air to the engine, and in combination with a boot provides control of noise emanating from the engine while being attached to and movable with the hood to provide access to the engine.

United States Patent 1 1 1111 3,800,910 Rose Apr. 2, 1974 [54] APPARATUS FOR DIRECTING AIR FLOW 1,183,670 5/1916 Riker 180/69 R AND SOUND WAVES 2,952,327 9/1960 Farr 180/69 R 2,701,024 2/1955 Thomas 181/33 K [75] Inventor: Jack H. Rose, Livonia, Mich.

[73] Assignee'. Massey-Ferguson 1nc., Detroit, Primary Examiner-Stephen .1. Tomsky Mich. Assistant Examiner-Vit W. Miska [22] Filed: g 2, 1972 Attorney, Agent, or Firm-Thomas P. Lewandowski [21] Appl. No.. 277,462 ABSTRACT 52 US. Cl. 181/35 A, 181/35 R, 181/40, enclosureai of a mid, attached 181/33 E 181/49 181/69 R hood or'cowlmg of a vehicle engine, having an air [5],] In. CL F01 1/00, Foln 5/00, b /00 inlet integral w1th the hood or cowlmg, combmes with 581 Field 01 Search 181/33 K 40 35 A the Passages for 0f combusion Isl/35 R 6 6 69 to the engine as it passes through the mold. The mold provides cold air to the engine, and in combination [56] References Cited with a boot provides control of noise emanating from UNITED STATES PATENTS the engine while being attached to and movable with the hood to provide access to the engine. 3,249,172 5/1966 De Lorcan /69 R 2,881,860 4/1959 9 Claims, 5 Drawing Figures Ternes 180/69 "ATENTED APR, 2 I974 SHEET 3 [IF 3 APPARATUS FOR DIRECTING AIR FLOW AND SOUND WAVES It has been a recognized problem in vehicles driven by engines that proper tuning of the engine will be aggravated by hot air being supplied to the engine, particularly in two-cycle engines, for example, those used on snowmobiles. One reason for the above problem in snowmobiles has been the location of the carburetor under the cowling or hood. The location under the hood often arises so as to remove the carburetor from the immediate vicinity of the driver. The entrapped air between the cowling and the engine is heated by the engine before it can enter the engine as combustion air.

One consideration in location of the carburetor arises from its noise level and the transmission of this noise to the driver as well as the surrounding environment in light of recent government regulations on allowable noise levels.

One approach to solving the above problems has been to enclose the opening to a carburetor located beneath the cowling with a type of silencer mounted on the carburetor and in turn directed to an opening in the vehicle body from which fresh air could be drawn. Since the silencer was attached to the carburetor, it could not also be attached to the cowling to obtain an opening to receive fresh air if the cowling was to be removable or movable relative to the engine for servicing the engine. Thus, another problem arose, in crossing over the engine to openings in the vehicle the configuration of the silencer was such as to cover the engine making the engine inaccessible, even with the cowling raised or removed, unless the silencer was dismantled.

Another problem with attempting to silence the operation of vehicle engines is the complexity of the device or apparatus used. The complexity is such as to require the device or apparatus to be fabricated, at least to a partial extent, for all the prior art devices or apparatus.

Contributing to the complexity of the above devices are devious air flow passages incorporated therein as a means of filtration to control noise level. Providing passages which require the flow of air to change direction suppresses the alternating flow of air, which is the source of sound waves, without substantially impeding the steady flow of air needed to operate the engine.

In general, sound results from sound waves transmitted through the air. The waves have a frequency, normally expressed in cycles per second and are generated by vibrations of an object in contact with the air generally referred to as sound radiation. Sound intensity is measured in decibels and is inversely proportional to the area of propagation. Thus, the greater the area into which the sound radiates the lower the intensity, making chambers such as plenums useful for reducing the intensity of a sound. The loudness ofa sound is determined by comparing to a loudness level, normally measured in phons which is a sound of given intensity at a given frequency.

Control of sound, or more particularly noise, can be accomplished by isolation and transmission isolation methods in addition to filtration methods. Isolation is the prevention of one portion of a machine or structure from setting another portion into vibration which may be a more effective radiator of sound. For example, the

vibrations of an engine should be prevented from setting the cowling of the vehicle in which the engine is mounted into vibration with the engine. Similarly, if air with alternating flow can be confined, for instance in a chamber, then the vibrations or sound Waves are restricted in their ability to transmit sound.

Transmission isolation is an additional aid to control more particularly oriented to transmission through so]- ids as opposed to fluids whereby elastic discontinuities may be introduced into structures in which sound transmission is a function of the density and sound velocity for the material involved. Thus, in our example of the engine and the cowling if a direct connection were made between the two it would allow transmission along and through the connector. Introduction of an elastic discontinuity in the connector itself or in addition to the connector would decrease the effectiveness of the connector as a sound transmitter.

The last problem, but by far not the least, is the increased cost of the additional materials to solve the above problems. As mentioned previously, the prior art devices are complex and require considerable materials which must be at least partially fabricated all of which substantially increase cost.

The present apparatus for directing combustion air going to and sound waves emanating from an engine solves the above problems. The apparatus includes an enclosure attached to an air inlet integral to the covering over the engine and a boot for interconnecting the enclosure to the engine. Mounting the enclosure on the covering allows it to move with the covering to provide free access to the engine While the engine is provided cold air from the air inlet. By incorporating the inlet in the covering the enclosure is simplified. Use of the covering to form air passages between the covering and enclosure eliminates the requirement for fabrication. The boot alleviates the problems of noise transmission to the covering and lowers the requirement for dimensional tolerance between the engine and the enclosure.

The elimination of fabrication on the enclosure combined with a reduction in material on the present apparatus because of its simpler design in extending to the covering rather than the vehicle body, results in a substantial cost savings over the prior art devices.

The present invention relates to apparatus for directing combustion air going to an engine and sound waves emanating from the engine and more particularly to apparatus incorporated with and attached to a covering over the engine. An air inlet for admitting cold air located in a cavity in the covering connects to an opening in one end of the enclosure, and the enclosure extends toward the engine where another opening is provided in the enclosure. Means for fluidly sealing the other opening to the engine are also provided.

In one embodiment, an open faced mold, having an opening in the end opposite the open face portion, forms the enclosure. The open face of the mold has a configuration to match with the cavity containing the air inlet to which it is attached, and thereby forming passages of a devious nature for directing combustion air to the engine. The passages filter the sound waves emanating from the engine by redirecting them to muffle the noise. A boot of flexible material provides the means of connecting the mold to the engine and allows the mold to travel with the covering when the covering is moved relative to the engine to provide access thereto. The mold incorporates a plenum and may include directing vanes and ram tubes'to further direct air flow to the engine. The plenum also provides a greater area of propagation for sound waves to help reduce the loudness of noise emanating from the entry to the engine.

FIG. 1 is a fragmentary elevational view of a vehicle incorporating apparatus in accordance with the present invention having portions broken away to reveal greater detail;

FIG. 2 is an enlarged view of a portion of the vehicle illustrated in FIG. 1 better illustrating the apparatus incorporated therein with further portions thereof broken away to reveal further detail;

FIGS. 3-5 are cross-sectional views of the apparatus cowling or hood 20, by a plurality of bolts and nuts 22 and 24 as best illustrated in FIG. 2. As will be subsequently described in greater detail, the mold 18 combines with a portion of the hood adjacent it to form passages for directing the flow of cold air entering an inlet 26 to the carburetor 14. In the embodiment illustrated, the inlet 26 is in the form of a pair of slots 28 (best illustrated in FIG. 4) in an identation in the hood 20. One skilled in the art would be aware of numerous modifications which could be made to the size, shape and orientation of the inlet 26 to suit other engine and covering applications. Modifications to the boot 16 will also be apparent to one skilled in the art. Other means of sealing the enclosure to the engine 12 could be, for example, a flexible hose. Further, the sealing means could be attached to the enclosure as well as the engine 12,.partic ularly in otherembodiments where it may not be as practical to attach it to the engine involved.

The use of the mold 18 is particularly advantageous in the snowmobile where the engine 12 and particularly the carburetor 14 are adjacent the drivers position, indicated generally by the numeral 30. The mold 18 has the advantage of the ability to decrease the loudness of the noise experienced by the driver. A further advantage in use of the mold 18 is to direct cold air to the engine 12. The cold air is preferable over hot air which otherwise would be available beneath the hood 20 of the snowmobile having been subjected to the heat of the engine 12. The difficulty in'tuning the engine 12 when hot air is supplied is reduced when cold air is used to prevent detonation and overheating of the engine 12 under sustained full load performance.

Typically, the hood 20 is raised by pivoting it about the front of the snowmobile to expose the engine 12 for servicing. When the hood 20 is pivoted, the mold 18 moves with it and the boot 16 provides a parting line between the mold 18 and the carburetor The boot 16 is preferably made of flexible material with a degree of resilience to permit it to adapt to the shape and position of the mold. Rubber would be a good example of material suitable for the boot 16. The adaptability of the boot 16 to the position of the mold 18 results in a substantial lowering of the requirements of dimensional tolerance on the mold l8 and hood 20. Sealing of the air flow through the apparatus is also enhanced by the flexibility of the boot. The requirements of expansion provisions in interconnecting the hood 20 and engine 12 are also lowered. Control of noise emanating from the engine 12 is provided by the boot 16 in the form of transmission isolation. The transmission of the vibrations of the engine 12 to the hood are isolated by the elastic discontinuity of the boot 16 to prevent the hood 20 from becoming a radiator for the noise of the engine 12.

Referring to FIGS. 1 and 2, a raised portion 32 of the hood 20 has its continuity broken by a surface 34 which is indented at a gradual angle as it approaches the inlet 26. The inlet 26 is located between the indented surface 34 and the top of the raised portion 32 in a nearly vertical plane which facilitates the entry of air into the inlet 26. The sides 36 of the raised portion 32, one of which can be seen in FIG. 2, drop below the upper portion of the mold 18 immediately adjacent the mold 18 as illustrated in FIG. 4. The inlet 26, sides 36 and a rib boss 38, on the underside of the raised portion 32 of the hood 20, form a cavity for receiving the mold 18. Protruding at generally a right angle from the hood 20, the rib boss 38 is a continuous member extending between the sides 36 of the raised portion 32 generally paralleling the inlet 26. A plurality of tapped holes 40 are provided in the rib boss 38 for receiving the bolts 22. Similarly, a series of bosses 42 having tapped holes 44 therein are provided beneath the identical surface 34 adjacent the inlet 26. t

The mold 18 has a raised inner portion 46 which is positioned adjacent the the inlet 26.

The mold 18 has a raised inner portion 46 which is positioned adjacent the top of the raised portion 32 when the mold 18 is placed within the cavity of the I hood 20. A seal 48 may be inserted between the hood 20 and the mold 18 to militate against the flow of air across the mating line between the raised inner portion 46 of the mold 18 and the hood 20. Preferably, the seal is air imperious and applied to the mold 18 with an adhesive. When the raised inner portion 46 is considered together with a pan shaped portion 50 of the mold 18, it will be found that passages for directing air flowing in the inlet 26 are formed between the pan and raised inner portions 50 and 46 of the mold l8 and the cavity in the hood 20.

The pan portion 50 of the mold is illustrated in FIG. 2 having a bottom, front and rear walls 52, 54 and 56, respectively, from which front and rear flanges, 58 and 60 respectively, extend outwardly from and generally parallel to the bottom wall 52. The flanges 58 and 60 provide a seat for the nuts 24 which fasten the mold 18 to the hood 20.

A rear passage 62 and a portion of a front passage 64 can be seen in FIG. 2. Side passages 66 can be seen in FIG. 4 as formed by the bottom wall 52, side walls 68, sides 36 and top of the raised portion 32 of the hood 20 and the raised inner portion 46 of the mold 18. The closeness of the side walls 68 to the sides 36 of the hood 20 effect an air seal between them.

The devious flow path of air flowing through the passages is best illustrated in FIG. 3 by arrows showing the direction of flow which is split upon entering the two openings 28 in the inlet 26 (see FIG. 4) and upon contact with the raised inner portion 46 of the mold 18. The front passages 64 have cross sections which diverge from the center of the incoming stream to each side of the mold 18 to accommodate the accumulation of air across the face of each opening 28 in the inlet 26. The air diverted by the raised inner portion 46 enters the side passages 66 and is further directed to the rear passages 62 which converge at an entry 70 before entering a plenum 72. The entry 70 is an opening in the raised inner portion 46 which converges downwardly to direct theflow into the plenum. The angle of convergence may be varied in accordance with the system resistance experienced.

. Expansion of the air, upon entering the plenum decreases the velocity of the air in the plenum resulting in less turbulence in the air leaving a discharge port which is a circular opening 74in the bottom of the plenum 72 in the embodiment illustrated. The opening connects to the boot 16 to direct the air to the carburetor l4 and could be other than circular in shape.

The mold 1 8 is adaptable to receive air vanes 76 which may be added to further assure a laminar flow of air enters the carburetor 14 by breaking up any tendency of the air to swirl in leaving the opening 74. An alternative to the air vanes 76 would be a tuning tube, not illustrated, which would be inserted into the opening 74 to form an annulus therebetween. The tuning tube could be accommodated for mounting in the mold 18 or on the carubretor l4, and further, air vanes could be added to the annulus formed between the tuning tube and discharge port of the mold 18.

It should be noted that the above described passages 62-66 for the flow of air are generally maintained in the cavity of the raised portion 32 of the hood 20 with at least one side of the passages 62-66 being a portion of the hood 20 which is shielded from the engine heat. Thus, the air in the passages is maintained cool in passing through the passages. Both the cross-sectional area of the openings 28 in the-inlet 26 and that of the area of passages combining to supply air to the carburetor 14 should be greater than the entry area ofthe carburetor 14. g

Referring to FIGS. 24 the shape of the mold 18 while somewhat intricate is such as to enable it to be cast in one pieceQparticularly because the tops of the passages-62-66 are formed by the hood 20 to enable the mold 18 to be formed with an open face as a single piece mold. The raised inner portion 46 of the mold 18 is formed by raising a part of the pan bottom wall 52 around the periphery of the plenum 72 upward to a position adjacent the top of the raised portion 32 of the hood 20. The portion immediately adjacent the hood 20 is flat forming a ridge 78 to accommodate the seal 48. The ridge 78 encompasses the top of the plenum over its entire periphery except for that part where the entry 70 exists. As a result of the above construction, the entry 70 is completely shielded from the inlet 26. Downwardly extending outer and inner partitions 80 and 82 extend over the periphery of the raised inner portion 46 from the ridge 78. The spacing and orientation of the partitions is a function of the desired position of the plenum 72, and the requirements for making a practical and satisfactory mold 18.

The outer partition 80 interconnects the ridge 78 with the flange 58 at the front of the mold 18 in the area adjacent the middle boss 42 (see FIG. 3), and with the bottom wall 52 along the remainder of the front as well as the sides and'rear of the mold l8. Extending down beyond the bottom wall 52 the inner partition 82 forms the sides of the plenum 72. FIG. 2 illustrates a projection in the rear portion of the sides of the pienum 72 to form the extended partition 84 immediately below the entry 70. In FIG. 3, the end partitions 86 interconnecting the inner and outer partitions 82 and extend down below the bottom wall 52 in legs 88 which interconnect the inner partition 82 with the extended partition 84. The end partitions converge upon each other but do not meet at the bottom of the plenum resulting in the extended partition 84 having a V-shape with a flat bottom which acts as a stiffener to prevent flexing of the rearward portion of the inner partition 82 while providing a larger entry to the plenum 72 and directing the air flow toward the center of the plenum 72. FIG. 5 best illustrates the V-shape of the extended partition 84 which preferably corresponds to the convergence of the entry 70.

FIG. 4 illustrates the shape of the bottom of the plenum 72 which includes an inclined surface 90, and a generally horizontal transitional surface 92 which together direct the flow of air to the opening 74. A snout 94 connects the opening 74 to transitional surface 92 and has a right cylindrical portion 96 and a conical portion 98. Placement of the conical portion 98 at the proper angle to the cylindrical portion 96, as illustrated in FIG. 2, brings the snout 94 into seating alignment with the boot 16. Seating and sealing are both enhanced by the taper of the conical portion 98 which permits insertion of the opening 74 of the snout 94 into the opening in the boot 16. The conical portion 98 also serves to house the air vanes 76 which are rotated 45 out of phase, in FIG. 2, to present them in true profile. The vanes 76 have basically rectangular faces with a taper 100 on each end to conform them to the shape of the conical portion 98 and a chamfer 102 on the corners opposite the taper 100 to permit clearance between the vanes 76 and the cylindrical portion 96 as at 104. Protrusions 106 may be added to the vanes to aid in securing their position within the snout 94. The protrusions 106 mate with recesses 108 in the conical portion 98, as best illustrated in FIG. 1. Preferably, the vanes'76 are made of the same material as the mold 18 and may be permanently attached by a suitable adhesive. An example of a suitable material for the mold would be ABS-LE cycolac, others could be used.

Noise and noise control is a science complicated by many variables which are often of a nature defying isolation making it difficult to measure a level of noise. As a result, the specific point of improvement or the most effective element in obtaining a quieter application often cannot be stated with certainty. It is possible, however, to point out particular features which are amenable to the basic principles of noise abatement and present in the apparatus described above.

Viewing the devious flow paths for the air traveling in the passages 6266, described above with respect to FIG. 3, it can be seen that the alternating flow or sound waves in the air which attempt to travel back through the passages will be subjected to filtration at each degree turn in the path leading back to the inlet 26. Further, the splitting of the passages 62-66 permits the placement of the entry 70 to the plenum in a manner completely shielding it from'the inlet 26. The mold 18 itself, of course, isolates vibrations of the air by confining the alternating air flow emanating from the carburetor 14 within the mold 18. Further, the intensity of the sound is lowered by the large area of propagation provided by the plenum 72 over which the sound waves may be dispersed before being transmitted out the inlet 26.

It should also be noted that the inlet 26 is positioned to direct any sound emanating therefrom in a direction opposite to that of the operators station 30, see FIG. 1.

An actual test Comparing the noise with the above apparatus mounted on an engine with that when the apparatus was removed showed a reduction of up to 3 dbA or approximately a 25 percent reduction in noise level.

Thus, even though a direct connection was made between the engine and the hood thereover, the use of the above apparatus reduced the noise level below that of the engine and covering alone.

In addition to the above advantages with respect to directing air flow and sound waves, the above apparatus has the advantage of lower cost over prior art apparatus ofa fabricated nature in that the mold 18 does not require fabrication but is molded in a single piece. Further cost reduction comes from direct connection of the mold 18 to the hood 20 which is a simplification over the more complex approach of extending to inlets in the side of the vehicle body for instance. At the same time, the simplicity of the mold 18 makes it readily adaptable to mounting on the hood 20 for movement with the hood 20 when the hood is raised to part the apparatus at the boot 16 as described above.

It is to be understood that the mold 18 is adaptable to other engine and hood configurations while maintaining its characteristics of devious flow paths, shielding of the entry from the inlet, a plenum, snout and the open face combining with the configuration of the hood. The offset ofthe snout 94 in FIG. 4 is an example of this type adaptability to accommodate a centered inlet 26 with an offset carburetor 14.

In accordance with the provisions of the patent statutes, the principal and mode of operation of the apparatus have been explained and what is considered to represent its best embodiment has been illustrated and described. It should, however, be understood that the invention may be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.

What is claimed is:

1. In a vehicle having an engine with a covering and an inlet therein, apparatus for directing combustion air going to and sound waves emanating from the engine comprising: a single piece enclosure attached to and movable with the covering having an opening therein; an open face on said enclosure for engagement with the covering, said enclosure including an inner portion within and spaced from the outer periphery of said open face extending toward the covering to form passages for directing the flow of air, and extending away from the covering to form a plenum for receiving said flow of air from said passages and slowing the velocity of incoming air directed to the engine while also dispersing sound waves; and means for sealing by contact the opening of said enclosure to the engine, said open face of said enclosure being connected to the inlet to cause outside air to be directed to the engine and to isolate the sound waves traveling through said enclosure.

2. The apparatus defined in claim 1 wherein said enclosure includes an entry internal of said enclosure for passage of air to the opening of said enclosure, said entry located in said inner portion extending toward the covering to permit shielding said entry from the inlet by said inner portion to reduce the noise level at the inlet originating from said entry.

3. The apparatus defined in claim 1 wherein said enclosure includes a snout containing the opening in said enclosure.

4. The apparatus defined in claim 1 including a seal for sealing a portion of said enclosure to the covering.

5; The apparatus defined in claim 1 wherein said means for sealing includes a boot for selectively sealing the connection of said boot to said enclosure to permit said enclosure to move with the covering.

6. The apparatusdefined in claim 1 wherein said enclosure is adaptable to receive air flow directing vanes located within said opening of said enclosure.

7. The apparatus defined in claim 1 wherein said enclosure is a single piece mold and said sealing means is a boot, said inner portion including a ridge, said ridge encompassing the upper portion of said plenum and being connected thereto by an inner partition, said mold further including an outer partition and a pan shaped portion, said outer partition interconnecting said ridge with said pan, at least a portion of the perimeter of said inner and outer partitions being cut away to form said entry into said plenum above said pan, said outer partition, pan shaped portion and the covering combining to form devious passages for the flow of air from said inlet.

8. The apparatus defined in claim 7 including a snout on said plenum having cylindrical and conical portions, said conical portion adapted to seat within said boot.

9. In apparatus for a vehicle with an engine and a covering therefor, the apparatus directing combustion air going to and sound waves emanating from the engine and being located between the covering having an inlet therein and means for sealing the apparatus to the engine, a single piece mold comprising: an open face on said mold for engagement with the covering; an inner portion within and spaced from the outer periphery of said open face extending toward the covering to form passages for directing the flow of air; a plenum formed by extending said inner portion away from the covering for slowing the velocity of incoming air and dispersing sound waves; and an entry internal of said mold located in said inner portion to shield said entry from the inlet by said inner portion to reduce the noise level at the inlet originating from said entry. 

1. In a vehicle having an engine with a covering and an inlet therein, apparatus for directing combustion air going to and sound waves emanating from the engine comprising: a single piece enclosure attached to and movable with the covering having an opening therein; an open face on said enclosure for engagement with the covering, said enclosure including an inner portion within and spaced from the outer periphery of said open face extending toward the covering to form passages for directing the flow of air, and extending away from the covering to form a plenum for receiving said flow of air from said passages and slowing the velocity of incoming air directed to the engine while also dispersing sound waves; and means for sealing by contact the opening of said enclosure to the engine, said open face of said enclosure being connected to the inlet to cause outside air to be directed to the engine and to isolate the sound waves traveling through said enclosure.
 2. The apparatus defined in claim 1 wherein said enclosure includes an entry internal of said enclosure for passage of air to the opening of said enclosure, said entry located in said inner portion extending toward the covering to permit shielding said entry from the inlet by said inner portion to reduce the noise level at the inlet originating from said entry.
 3. The apparatus defined in claim 1 wherein said enclosure includes a snout containing the opening in said enclosure.
 4. The apparatus defined in claim 1 including a seal for sealing a portion of said enclosure to the covering.
 5. The apparatus defined in claim 1 wherein said means for sealing includes a boot for selectively sealing the connection of said boot to said enclosure to permit said enclosure to move with the covering.
 6. The apparatus defined in claim 1 wherein said enclosure is adaptable to receive air flow directing vanes located within said opening of said enclosure.
 7. The apparatus defined in claim 1 wherein said enclosure is a single piece mold and said sealing means is a boot, said inner portion including a ridge, said ridge encompassing the upper portion of said plenum and being connected thereto by an inner partition, said mold further including an outer partition and a pan shaped portion, said outer partition interconnecting said ridge with said pan, at least a portion of the perimeter of said inner and outer partitions being cut away to form said entry into said plenum above said pan, said outer partition, pan shaped portion and the covering combining to form devious passages for the flow of air from said inlet.
 8. The apparatus defined in claim 7 including a snout on said plenum having cylindrical and conical portions, said conical portion adapted to seat within said boot.
 9. In apparatus for a vehicle with an engine and a covering therefor, the apparatus directing combustion air going to and sound waves emanating from the engine and being located between the covering having an inlet therein and means for sealing the apparatus to the engine, a single piece mold comprising: an open face on said mold for engagement with the covering; an inner portion within and spaced from the outer periphery of said open face extending toward the covering to form passages for directing the flow of air; a plenum formed by extending said inner portion away from the covering for slowing the velocity of incoming air and dispersing sound waves; and an entry internal of said mold located in said inner portion to shield said entry from the inlet by said inner portion to reduce the noise level at the inlet origiNating from said entry. 